1. Field of the Invention
The present invention relates to a continuously variable transmission; and more particularly, to a continuously variable transmission having a main power pathway including the pulley member of the continuously variable transmission (CVT) and a second power pathway which by-passes the main power pathway and does not include the pulley member.
2. Description of Related Art
FIG. 1 illustrates a prior art CVT 1. As shown in FIG. 1, a torque convertor 4 transfers the power output from an engine 2 to an input shaft 6. A planetary gear unit 8 is connected to the input shaft 6 and to a secondary input shaft 6A.
The planetary gear unit 8 includes double pinion gears 11, a sun gear 12 in a gearing relationship with an inner one of the double pinion gears 11, a planetary carrier 10 for the double pinion gears 11, and a ring gear 16 in a gearing relationship with the outer one of the double pinion gears 11. The sun gear 12 is mounted on the secondary input shaft 6A. The planetary carrier 10 is connected to the input shaft 6, and a first friction element 24 selectively connects the planetary carrier 10 to the secondary input shaft 6A. A second friction element 18 selectively connects the ring gear 16 to the housing of the CVT 1.
A drive pulley 22 is mounted on the secondary input shaft 6A. The drive pulley 22 includes a fixed pulley member 34, and a movable drive pulley member 33.
The CVT 1 of FIG. 1 also includes a secondary shaft 30, an output shaft 40, and an output gear unit 53. The secondary shaft 30 includes a driven pulley 28 and a first gear 29 mounted thereon. The driven pulley 28 is operationally connected with the drive pulley 22 by a chain 26. The drive pulley 22, the chain 26 and the drive pulley 28 form a pulley member 21 of the CVT 1.
The output shaft 40 includes a second gear 42 and a third gear 44. The second gear 42 is in a gearing relationship with the first gear 29 to transfer power from the secondary shaft 30 to the output shaft 40.
The output gear unit 53 includes a gear train portion 70 and a differential unit 71. The gear train portion 70 is in a gearing relationship with the third gear 44 and the differential unit 71 to transfer power from the output shaft 40 to the differential unit 71. The differential 71 then transfers power to the driving wheels (not shown).
When operating in reverse, the second friction element 18 is engaged, while the first friction element 24 is disengaged. This causes the secondary input shaft 6A to rotate in the opposite direction in which the input shaft 6 rotates. The power from the engine is transferred from the input shaft 6 to the input shaft 6A via the planetary gear unit 8, from the secondary input shaft 6A to the secondary shaft 30 via the pulley member 21, from the secondary shaft 30 to the output shaft 40 via the first and second gears 29 and 42 and from the output shaft 40 to the differential unit 71 via the third gear 44 and the gear train portion 70.
When operating in the forward direction, the first friction element 24 is engaged, while the second friction element 18 is disengaged. The power is then transferred as discussed above with respect to operation in reverse.
Because the prior art CVT of FIG. 1 utilizes a planetary gear unit 8, the construction of the CVT is quite complex and costly.
European Patent Application 198,534 to Van der Veen discloses a CVT which simplifies the CVT structure by eliminating the need for a planetary gear unit. Additionally, EPO 198,534 discloses that the use of a secondary shaft, such as secondary shaft 30 in FIG. 1, increases the size of the CVT, and discloses a CVT which eliminates the use of a secondary shaft. FIG. 2 illustrates the CVT of EPO 198,534.
As shown in FIG. 2, a torque convertor 4 transfers the power output from an engine 2 to an input shaft 6. The input shaft 6 includes a fourth gear 106 fixedly mounted thereon and a drive pulley 100 freely rotatably mounted thereon. Freely rotatably mounted means that even though the drive pulley 100 is mounted on the input shaft 6, the drive pulley 100 does not rotate when the input shaft 6 rotates unless a third friction element 114 connects the drive pulley 100 to the input shaft 6.
The CVT of EPO application 198,534 also includes an output shaft 40, but no secondary shaft. The output shaft 40 includes a sixth gear 110 freely rotatably mounted thereon. The sixth gear 110 is in a gearing relationship with a fifth gear 108, and the fifth gear 108 is in a gearing relationship with the fourth gear 106. A fourth friction element 112 selectively operationally connects the sixth gear 110 to the output shaft 40.
The output shaft 40 further includes a first sprocket 116 and a driven pulley 102 mounted thereon. The driven pulley 102 is operationally connected to the drive pulley 100 via a chain 104. The drive pulley 100, the chain 104 and the driven pulley 102 form a pulley member 121 of the CVT.
The CVT further includes an output gear unit 53 which includes a differential unit 71 and a gear train portion 70. The gear train portion 70 includes a secondary sprocket 120 operationally connected to the first sprocket 116 by a chain 118.
In operation, the power from the engine can be transferred from the input shaft 6 to the output shaft 40 by engaging the fourth friction element 112 and disengaging the third friction element 114. Power then is transferred from the input shaft 6 to the output shaft 40 via the fourth, fifth and sixth gears 106, 108 and 110. Unlike the CVT of prior art FIG. 1, power from the engine will not be transferred to the output shaft via the pulley member 121.
A second alternate power pathway is created by engaging the third friction element 114 and disengaging the fourth friction element 112. In this instance, the power of the engine is transferred directly from the input shaft 6 to the output shaft 40 via the pulley member 121.
When by-passing the pulley member 121, the EPO application 198,534 uses fourth, fifth and sixth gears 106, 108 and 110. The use of multiple gears to transfer power between rotatable shafts has two disadvantages. First, the use of many gears results in a large amount of noise being generated. Second, gear elements do not absorb vibrations very well; and consequently, any shock experienced by the transmission will be readily transferred by the gear arrangement.